1. Field of Invention
The present invention relates to an optical fiber manufacture method, a preform manufacture method and a preform manufacture apparatus that can manufacture a preform and an optical fiber with reduced variation in their diameters.
2. Description of Related Art
FIG. 1 shows a conventional glass base material first elongating apparatus 400. A glass base material 102, which is a base material of an optical fiber, is usually elongated by the glass base material first elongating apparatus 400. This reduces the diameter of the glass base material 102, to produce a glass rod 106. The glass rod 106 has a diameter from 3 mm to 5 mm larger than the most convenient diameter to draw an optical fiber. The most convenient diameter for drawing an optical fiber is 30 mm to 80 mm.
A glass base material first elongating apparatus 400 comprises a heating furnace 100 that heats the glass base material 102 and a drawing chuck 104 that holds and elongates the heated glass base material 102. To elongate the glass base material 102, the glass base material first elongating apparatus 400 supplies the glass base material 102 to the heating furnace 100. Here the glass base material 102 is heated to approximately 2000° C. The first elongating apparatus 400 then holds the glass base material 102 by the drawing chuck 104, and draws the glass base material 102 from the heating furnace 100 downward continuously to form a glass rod 106.
FIG. 2 shows a configuration of a conventional glass lathe 110. The glass rod 106 made by the glass base material first elongating apparatus 400 undergoes secondary elongation by the glass lathe 110 to produce a preform 107. At this time, the diameter of the glass rod 106 is reduced to prescribed diameter. The glass lathe 110 comprises chucks 118 and 119 that hold the glass rod 106, a tail stock 116 which moves the chuck 119, and a heating source 122 which heats the glass rod 106. One side of the chuck 118 is fixed, and the other side of the chuck 119 movable. A traction force can be applied to the chuck 119. The glass rod 106, which is held by the chucks 118 and 119, is heated by the heating source 122. The heated glass rod 106 is elongated by moving the tail stock 116 which pulls the glass rod 106. The result is, the diameter of the glass rod 106 reduces to become the prescribed diameter.
There was the possibility of manufacturing bent glass rods 106 when using a conventional glass base material first elongating apparatus 400 to elongate the glass base material 102. Also, when using a conventional glass lathe 110 to elongate the glass rod 106 to manufacture the preform 107 further problems often arose. These problems included variation in the diameter of the preform 107 because the amount of gas provided to the heating source 122 and the speed of moving the tail stock 116 differed for each preform 107 produced.
When elongating a bent glass rod 106, which is made by a conventional glass base material first elongating apparatus 400, to make a preform 107 by the glass lathe 110, the diameter of the preform 107 varied. When manufacturing optical fibers by drawing a preform 107 with a varying diameter, the diameter of the optical fibers produced also varies. This makes it difficult to manufacture an optical fiber of high quality.